There are two classifications of differentials. The first and most widely used is the conventional differential. The second classification is the non-conventional differential. Each classification functions with varying degrees of efficiency. There are two functions performed by every differential. They are as follows;
I. Torque Application--Ability to convert energy received into rotational motion to one or more axles. PA1 II. Maneuverability--Ability to differentiate between opposing axles due to variance in wheel speeds. PA1 I. Torque Application PA1 II. Maneuverability
In the past non-conventional differentials have excelled over conventional differentials in torque application, but the conventional differential has excelled in the area of maneuverability. Listed below is a contrast between the two classifications of differentials and their varying degrees of efficiency.
A. Conventional Differential PA2 B. Non-conventional Differentials (Two Types) PA2 A. Conventional Differentials PA2 B. Non-conventional Differentials
1. Applies torque to the "least" resistive wheel. PA4 a. Probability of immobility is greatest with this type. PA3 1. Limited Slip Differentials PA4 a. This unit "transfers" torque to the most resistive wheel. PA3 1. Probability of immobility is less than with a conventional differential. PA3 2. Locking Type Differentials PA4 a. This unit delivers torque to all driveable wheels simultaneously. PA3 1. Probability of immobility is the least with this type. PA3 1. Allows for "rapid spin up" of one wheel resulting in either or both of; PA4 a. Broken axle. PA4 b. Excessive tire wear upon recontact of tire on road. PA3 1. Some non-conventional differentials operate "harsher" than others. The harsher the operation, the more noticeable are the below mentioned problems; PA4 a. Excessive tire wear due to harsh operation when maneuvering. PA4 b. Pinching or binding action occurring when maneuvering. PA4 c. Understeer when cornering under power. PA4 d. Fishtailing during inclement weather conditions (especially noticeable when incline and vehicle weight play a role).
It matters not whether a differential is of a conventional or non-conventional type, if it gears multiple axles together, then each axle is dependent upon the opposite axle. This is known as a "transferring" of speed and/or power. Whatever action occurs to one axle, causes the opposite axle to react. This has led to tragic results that is referred to as "rapid spin up".
When a differential is driven in a straight line with no variance, both axles revolve 100% at equal speeds. If a variance of 10% occurs, then the slower axle will rotate at 90% of the previous speed, while the faster turning axle will rotate at 110% of the previous speed. On a non-conventional differential this action can result in a pinching or binding action that causes "understeer" to occur. On a conventional differential if one axle becomes immobilized, then the opposite axle will increase 100% in excess of normal operating speed as the same r.p.m.'s are delivered.
In consideration of the two differentiating functions of torque application and maneuverability, it is apparent that no matter how much torque application one may attain, if safety in maneuverability declines, then a dangerous condition exists.